Hm, I seem to have misremembered the article in a manner that changes the matter somewhat. Here it is:

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The Crocrotta and the Leucrotta

...Chapter XXXII of Ctesias' [Indica] gives a report of the Cynolycus, or "dog-wolf"; Pliny (VIII, 30) gave that hypothetical animal the name Crocrotta, and said that "it can break any thing with its teeth, and instantly on swallowing it digest it with the stomach."

More precise than the description of the Crocrotta is that of the Leucrotta, or Leucrocrotta, in which some commentators have seen reflections of the gnu, others of the hyena, and others, a fusion of the two. It is, says Pliny, "a wild beast of exraordinary swiftness, the size of the wild ass, with the legs of a stag, the neck, tail, and breast of a lion, the head of a badger, a cloven hoof, the mouth slit up as far as the ears, and one continuous bone instead of teeth." This animal lived in Ethiopia (where there are also wild bulls armed with movable horns) and it is said that it could sweetly imitate the human voice.

From the description of the leucrotta, it is clear that it is the same leucrotta we know today (or at least a close ancestor thereof). But, from these descriptions, it's the crocrotta that has the capacity to devour shields. And its description as "dog-wolf" makes it clear that its anatomy is nothing like that of the leucrotta (which is about as far from either dog or wolf as you can get and still be quadrupedal), leading me to surmise that it would almost certainly be incapable of breeding with the leucrotta. So the leucrotta must have developed the ability to devour hard materials independently. Which would mean that we have two critters that both selected for that same trait, yet one died out while the other thrived.